China today poured 50,000 troops into Sichuan, about 1,000 miles south-west of Beijing, to find survivors as the count of missing people was put at 60,000.

A 2,000-strong contingent of troops rushed to plug "extremely dangerous" cracks in the Zipingku Dam upriver from the earthquake-hit town of Dujiangyan, state media said.

Disaster relief officials said 18,700 people were feared buried in Mianyang, Sichuan's second largest city, and a further 4,800 in Mianzhu.

At least 19 British tourists on a panda-watching tour remain unaccounted for today.

Among them are retired postmaster David Atkins, 63, and his wife Diane, 62, of Portchester, Hants.

They have not been heard from since the tremor struck on Monday as their coach travelled from Chengdu, Sichuan's provincial capital, to the Wolong nature reserve.

Foreign Office officials and holiday group Kuoni have been unable to contact the coach carrying the 19 tourists.

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Rescued: Hands reach out to help as a little girl is lifted tenderly from the rubble

Mr and Mrs Atkins' only daughter, Lisa Staples, 39, from Portsmouth, Hants, said: "I am so worried because we have heard nothing. The last time I spoke to my mum was on Sunday just after they flew out.

"Everybody we have phoned has been pleasant and taken information but can't or won't say if they are alive.

"We have to be positive but we just don't know."

A Kuoni spokesman said: "All lines of communication to the region are down and as such no further information is known at this time. We are working closely with the British Consulate in China," he said.

"The UK operations team and duty officer in conjunction with the Foreign and Commonwealth Office in the UK and China are continuing to try to make contact with the group and will provide updates as and when information becomes available."

At least 100 other Britons travelling in the province are safe and unhurt, according to British travel organisation Abta.

Uphill struggle: Soldiers from the People's Liberation Army carry shovels and medical supplies through a devastated town in Beichuan county

Missing: David and Diane Atkins from Hampshire were on a tour when the quake struck

An eight-strong rapid-response team sent by the Foreign Office to locate the missing Britons is thought to have arrived in the massive quake-struck city of Chongqing yesterday.

The Foreign Office has set up a phoneline for concerned relatives.

The scale of devastation became clearer as more rescuers walked into the hardest-hit areas of central Sichuan, finding towns where 80 percent of the population have fallen victim to Monday's magnitude-7.9 quake.

Rescuers found the city of Yingxiu in Wenchuan county - the quake's epicentre - "much worse than expected".

Of the town's population of about 10,000, only 2,300 survived, and 1,000 of them were badly hurt.

Emergency director He Biao said: "They could hear people under the debris calling for help, but no one could because there were no professional rescue teams."

China's official quake death toll rose from 12,335 to 14,866 today - but it was unclear how many of the 7,700 dead in Yingxiu had been included in the count - if any.

The toll was expected to rise further as rescuers reach other towns.

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A pregnant woman, pulled from rubble 50 hours after the quake, is lowered onto a stretcher

With the lifting of storms that have hampered aid efforts, military helicopters air-dropped food, drinking water and medicine to Yingxiu.

East of the epicentre in Hanwang, the smell of incense hung over a crowd of sobbing relatives who walked among some 60 bodies wrapped in plastic, some covered with tributes of branches or flowers.

The dead appeared to have come from a heavily damaged school and apartments.

Residents complained that delays in aid had caused more deaths in the immediate aftermath of the quake.

One man said his wife had been killed while watching television and his daughter had died when her school collapsed.

The child did not die right away and could be heard saying, "Please help me daddy, please rescue me," right after the earthquake, he said, but there were no authorities to save her.

At a middle school in Juyuan dozens of small bodies lay under tarpaulins on the basketball court.

The smoke of firecrackers filled the air as relatives lit them to protect the souls of the dead children from evil spirits.

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Desperation: Rescue workers bow their heads in grief or exhaustion at the roadside

Photographs showed arms and a torso sticking out of the rubble as dozens of rescuers worked to free the teenagers.

Large cranes and small mechanical winches were used while emergency workers scrabbled with their bare hands to move concrete slabs as horrified parents looked on.

Fifty pupils were confirmed dead as the rescue effort continued into the night.

"It was around 2:30pm and the building suddenly began to rock back and forth," one girl who managed to escape said.

Witnesses reported that they saw scores of pupils struggling to escape from debris.

Four more children died when two primary schools were crushed in the town of Chongqing. Nineteen pupils and teachers remained buried.

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Homeless: Shock and bewilderment shows on the faces of displaced earthquake victims

At a middle school in Beichuan, where about 1,000 pupils and teachers are buried in the ruins of a seven-storey building, parents waited while rescue work went on into the night.

Xinhua reported: "Many parents burst into tears when a rescuer carried a teenage girl out of the ruins. She had lost her legs."

A tearful mother said: "I just pray my child is safe. Who cares if our house has collapsed?"

The Chinese government's high-gear response is aimed at reassuring the population countrywide while showing the world the nation is capable of handling the disaster ahead of the Beijing Olympics in August.

Today's leg of the Olympic torch relay in the south-eastern city of Ruijin began with a minute of silence.

• The telephone number to check on people who may be affected by the earthquake is 0086 105 192 4499.